Do hazardous areas need an external ignition source?

Hazardous areas in general – and especially in terms of Zone 0, 1 and 2 designations – occur in the presence of a potentially combustible or explosive substance, often a gas, and in each of those zones, the correct hazardous area equipment is important to remove potential external sources of ignition.

But containment is also crucial as not all combustible substances need an external ignition source, including clouds of fine particles that take on some of the properties of an explosive gas.

Incidents like the Bosley flour mill explosion in Cheshire in 2015 highlighted the risks posed by airborne dust, which can ignite and explode with disastrous and tragic consequences.

Now newly published research in IEEE Transactions on Industry Applications warns that the spark that triggers such an explosion can come from the dust cloud itself.

“Divided solid substances dispersed into a dust cloud, for example into a silo, can form a potentially explosive atmosphere, if in the right concentration with the oxidising agent, e.g. air,” the researchers write.

“In addition, it is known that the pneumatic handling of the substance, which allows its transport at a certain velocity, can generate static charges; thus, a possible competent ignition source may be also created.”

In effect, the static charge caused by the moving dust cloud can spark its own explosion – an extra risk to be accounted for when choosing hazardous area equipment to not only avoid igniting a blast, but also to contain one if the cloud should happen to self-ignite.